One way could be through a time - travel plot. Maybe Hermione travels back in time and ends up in a relationship with Fred instead of Ron, and then the pregnancy occurs. Another option is a magical accident where a spell affects their emotions and actions towards each other, leading to the situation.
Perhaps in a parallel universe where the rules of attraction and relationships are different in the wizarding world. Fred and Hermione could be fated to be together in this universe, and the pregnancy could be a natural result of their relationship. The fanfiction could then explore how this different universe's Hogwarts deals with such a situation compared to the original.
A fanfic writer could make it plausible by creating a new magical lore. For example, there could be a new potion that causes unexpected attractions and consequences, which Fred and Hermione unknowingly consume. This would then lead to their relationship and the pregnancy. It would require a lot of world - building though.
Well, it's a wild fanfiction concept. Fanfic writers might play with the idea by having some sort of magical mix - up or a different relationship path for Hermione. Maybe there's a spell gone wrong that leads to this unexpected pregnancy. But it would surely be a huge departure from the original story's themes and relationships.
Perhaps it's a result of some dark magic interference. The story could focus on how Harry and Hermione struggle to find a way to reverse it at first. But as time goes on, they start to form an unexpected bond with the unborn child in a magical way. They might face discrimination or suspicion from some in the Hogwarts community who fear the unknown nature of this magical pregnancy, and they have to prove that they can handle it and that it's not a threat to the school.
One reason could be that they played a particularly mischievous prank on her that went too far. For example, if they made her late for an important exam or meeting with a professor by using one of their wild magical inventions. Hermione, being a stickler for rules and academic achievement, might lose her temper and hex them in retaliation.
Fred could use his knowledge of the Weasley family's magic tricks and inventions. He might have some secret gadget or spell that can break through the barriers or spells that are being used to torture Hermione.
Well, in fanfiction, it's often about bending the rules. Maybe it could be some sort of magical accident. For example, a misfired spell that had some unexpected consequences on their relationship and led to this situation.
In many fanfictions, a plot where Hermione is pregnant at Hogwarts can bring a whole new set of challenges and storylines. It might involve how she manages her studies while dealing with the physical and emotional changes of pregnancy. Also, it could explore how her friends, like Harry and Ron, react to this unexpected situation.
One way could be through a time - travel plot. Maybe some magical accident sends Hermione back in time and she ends up in a relationship with Draco. Their different backgrounds would create a lot of tension. For example, Hermione's Muggle - born status and Draco's pure - blood family values. But as they get to know each other better, they fall in love and then the unexpected pregnancy occurs. This would shock the Hogwarts community as they are from rival houses and different social circles.
Draco Malfoy could be a likely antagonist. He might be jealous of the friendship or whatever relationship is developing between Fred and Hermione and try to cause trouble for them. Another could be some of the more strict professors who don't approve of their unorthodox ways of doing things.
Well, Hermione's usually logical and rational, but the pregnancy can make her more emotional at times. This is a new side of her that the fanfiction can explore. Fred, on the other hand, may find himself having to grow up quickly. He has to think about providing for his family now, which is a big change from his carefree days at Hogwarts.
Fred's reaction could be a complex mix of emotions. On one hand, he might be overjoyed at the thought of having a child with Hermione. He may immediately start making plans for their future as a family. However, he could also be a bit worried. After all, having a baby is a big responsibility. But his natural optimism would likely shine through, and he'd assure Hermione that they can handle it together. He might also crack a few jokes to lighten the mood, saying something like 'Our baby will be the most mischievous one in Hogwarts before we know it!'